1. Field of the Invention
The present invention relates to an electret condenser microphone and, more particularly, to an electret condenser microphone that is improved in performance by a fixed electrode plate increased in size and a back chamber increased in volume.
2. Description of the Related Art
FIG. 1 shows a conventional electret condenser microphone. The conventional electret condenser microphone 100 includes a cylindrical metal case 11, a conductive polar ring 12a, a diaphragm 12b, a spacer 13, a fixed electrode plate 14, a ring-shaped insulting base 15, a ring-shaped conductive base 16, and a printed circuit board (PCB) 17 on which circuit components and a connection terminal is formed. The polar ring 12a and the diaphragm l2b may be integrated with each other as a single diaphragm plate 12. The fixed electrode plate 14 includes a conductive metal plate 14b coated with a polymer film 14a on which an electret is formed.
In such a conventional electret condenser microphone 100, since the insulating base 15, insulating the fixed electrode plate 14 from the case 11, is formed to be relatively thick to provide sufficient supporting force, the size of the fixed electrode plate 14 is limited. In addition, since the conductive base 16 is disposed inside the insulating base 15, a volume of a back chamber is reduced, deteriorating the performance of the microphone. That is, since the conventional electret condenser microphone 100 is designed in a dual-ring structure where the ring-shaped conductive base 16 is fitted in the ring-shaped insulating base 15, an inner diameter of the conductive base 16 is reduced to thereby reduce the volume of the back chamber. Furthermore, in some cases, the fixed electrode plate 14 may be assembled by being fitted in the insulating base 15. In this case, a size of the fixed electrode plate 14 is reduced, as a result of which a size of the diaphragm 12b opposing the fixed electrode plate 14 is also reduced, thereby deteriorating acoustic properties such as sound sensitivity and frequency response.